The principles on which the present apparatus is based are well known in the prior art. For instance, the concept of making a treatment plant using aeration to sustain the bacterial digestion of wastes for small communities has been extensively discussed in a 1966 publication of the National Sanitation Foundation of Ann Arbor, Mich., entitled "Package Plant Criteria Development" based on a study made for the Federal Water Pollution Control Administration, Demonstration Grant Project WPD-74. Moreover, the concept of bubbling air through the sewage in a manner to make it circulate is known in the prior art as evidenced by U.S. Pat. Nos. 3,348,687 to Foster; 3,627,136 to Mackrle and 3,809,245 to Kennedy, these patents using such circulation to promote centrifugal separation of solid particles from the sewage so that relatively clearer water can be removed as an effluent. The copending patent application of Peasley and McKinney, Ser. No. 579,176 filed May 20, 1975, now U.S. Pat. No. 3,984,322, and entitled "Sewage Treatment Apparatus" shows an aerobic bacteria sewage treatment apparatus using compressed air to aerate waste water mixed with activated sludge, and to cause it to circulate about a cylindrical clarification compartment placed in a tank and having means to provide a zone of relative quiescence in the circulating sewage from which the clarification compartment withdraws water and further separates solid matter therefrom, finally delivering a well clarified effluent, the effluent being withdrawn from the top of the clarification compartment above a filter bed whereby the effluent is substantially free of solid matter. The copending patent application of Howard Peasley, Ser. No. 641,867 filed Dec. 17, 1975 and entitled "Apparatus for Treating Sewage" adds, among other features, the concept of periodically using the compressed air source to back-flush the clarification compartment and filter means therein, to purge the latter and increase the operating efficiency of the apparatus, doing so at a time when the apparatus is experiencing minimum influx of new sewage for treatment.